As the U.S. space program turns to focus on planetary surface exploration, there will be an increasingly important role for extended simulations at analog field sites. Field testing and training date back to the Apollo program, and have been pursued with increasing scope and concerns of fidelity during the past decade. These recent tests have included considerations of exploration for minor bodies, but in the whole have been more applicable to lunar and Mars missions. In simulating extravehicular activities (EVAs), a variety of pressure suit analogs have been adopted in the past, ranging from a full pressure suit to no special garments at all. Simulating an EVA on Mars or, more challenging, the moon realistically in the field on Earth is an effectively impossible task. The “gold standard” would be a pressurized suit, but even without life support equipment, the suited subject weighs substantially more than they would on a mission, massively increasing physiological workload and incurring increased physical risks to the subject. To attempt to improve Earth-based fidelity while supporting field testing, the University of Maryland has developed three successive series of suit simulators using garment design and interstitial padding to represent the bulk and joint limits of a pressure suit without pressurization. This allows the use of a lighter-weight suit, more representative of the on-back weight for a suit system for the moon or Mars, without incurring the training and safety monitoring requirements of a pressurized system. Helmets of these suits are totally enclosed with ventilation fans to provide fresh air to the wearer, simulating the aural environment of a pressurized suit with vent air noise in the helmet. Since the suit garment very effectively insulates the subject, these systems also had to be designed to incorporate a liquid cooling garment and ice reservoir in the backpack assembly. These suits were used in a series of field tests in Arizona in collaboration with Arizona State University, where professional geologists performed field research while in the suits in simulation of lunar or Mars scientific exploration. In the last two years, the UMd suit simulators have become an integral part of operations at the HI-SEAS field site in Hawaii. These tests are isolation studies, requiring the six-person crews to operate without any physical or visual interactions outside of the simulation, and requiring environmental isolation whenever an EVA simulation takes place. To date, two MX-C suit simulators have accumulated over six months of operational use in support of three successive missions. During the HI-SEAS tests, EVA operations are conducted in either MX-C suit simulators or in off-the-shelf hazardous material handling (HAZMAT) suits. The HAZMAT suits are lighter in weight, not overly restrictive of limb motion, and allow unrealistic capabilities such as pulling the arms inside and using a tablet inside the suit. The paper focuses on the lessons learned from EVA simulations performed in the second and third HI-SEAS missions using the MX-C suit simulators. Critical issues with the MX-C suits, including the need for assistance in doffing and donning the suits, and inability for self-rescue in the event of overheating or trauma. Desirable design revisions for the next generation suit simulators based on lessons learned are presented and prioritized.